Objective: To evaluate clinico-pathological features and prognostic valuses of Endometrial stromal sarcomas (ESS) through comparison of the two grade groups (low- and high-grade disease).Methodology: We retrospectively analyzed the medical records of 27 patients who were diagnosed with ESS at a single institute between March 1988 and November 2009. Our retrospective chart review was approved by our local institutional Review Board (IRB).Results: The median age of the patients was 44.0 years, the median follow-up period was 101.0 months and the 10-year survival rate was 74.2%. The median uterine weight was 215.0 gm. Twenty-three (70.4%) and four patients (29.6%) had low- and high-grade disease, respectively. As primary treatment, twenty-four (70.4%) and three patients (11.1%) underwent type I hysterectomy and type III hysterectomy, respectively. Total six cases were recurred and two cases of the six-recurred patients were distant metastasis (lung) and four cases were died of the disease. Univariate analysis revealed that the histologic grade and the uterine tumor weight were significantly related with longer disease-free survival (p=0.025 and 0.043 respectively).Conclusion: ESSs with high-grade or larger tumor size have to be carefully and sufficiently managed, because of its rarity and aggressive behavior. To determine the proper adjuvant treatment of ESS with high risks, further clinical data should be collected and studied.